Winter Storm Outlook

Issued 3-7 days in advance for anticipated snow/ice.

Blizzard Warning

A Blizzard Warning means that the following conditions are occurring or expected within the next 12 to 18 hours.
1) Snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer

AND
2)  Sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater.
There is no temperature requirement that must be met to achieve blizzard conditions.

Winter Storm Warning

A Winter Storm Warning is issued when a significant combination of hazardous winter weather is occurring or imminent.

Significant and hazardous winter weather is defined as a combination of:
1)  Over 5 inches of snow/sleet
AND/OR
2)  Glaze accumulation (freezing rain) of 1/4 inch or more
AND/OR
3)  Enough ice accumulation to cause damage to trees or powerlines.
AND/OR
4)  a life threatening or damaging combination of snow and/or ice 
accumulation with wind.

Ice Storm Warning

¼ inch or more of ice accumulation.

Freezing Rain Advisory

Ice accumulations of less than 1/4 inch.

Winter Storm Watch

A Winter Storm Watch is issued when there is the potential for significant and hazardous winter weather within 48 hours. It does not mean that significant and hazardous winter weather will occur...it only means it is possible.

Significant and hazardous winter weather is defined as:
1)  Over 5 inches of snow (and/or sleet)
OR
2)  Glaze accumulation (freezing rain) of 1/4 inch or more
OR
3)  Enough ice accumulation to cause damage to trees or powerlines.
OR
4)  a life threatening or damaging combination of snow and/or ice accumulation with wind.

Winter Weather Advisory

A Winter Weather Advisory will be issued when 2 to 4 inches of snow, alone or in combination with sleet and freezing rain, is expected to cause a significant inconvenience, but not serious enough to warrant a warning. If the event is expected to impact the Baltimore/Washington metro areas during rush hours (4-9 am or 2-7 pm on weekdays) forecasted snow totals of one inch will necessitate the issuance of a winter weather advisory.

Freeze Warning

A Freeze Warning is issued when significant, widespread freezing temperatures are expected.

A Freeze Warning is issued in the autumn until October 15th west of a line from Frederick, Maryland to Charlottesville, Virginia.  It is issued in the autumn until 
November 1st east of that line.

A Freeze Warning is issued in the spring when it is late enough to cause damage to new plants and crops.

Frost Warning

A Frost Warning is issued when significant, widespread frost is expected.

A Frost Warning is issued in the autumn until October 15th west of a line from Frederick, Maryland to Charlottesville, Virginia. It is issued in the autumn until November 1st east of that line.

A Frost Warning is issued in the spring when it is late enough to cause damage to new plants and crops.

Wind Chill Advisory

A Wind Chill Advisory is issued when wind chills of -5F to -19F are expected.

Wind Chill Warning

A Wind Chill Warning is issued when wind chills of -20F or lower are expected.

Dense Fog Advisory

A Dense Fog Advisory is issued when widespread fog is expected to reduce visibilities to 1/4 mile or less over a large area for an extended period of time (more than 3 hours).

High Wind Watch

A High Wind Watch is issued when the following conditions are possible:

1) sustained winds of 40 mph or higher for one hour or more

OR

2) wind gusts of 58 mph or higher for one hour or more.

High Wind Warning

A High Wind Warning is issued when the following conditions are occuring or imminent:

1) sustained winds of 40 mph or higher for one hour or more

OR

2) wind gusts of 58 mph or higher for one hour or more.

Hurricane Watch

A Hurricane Watch is issued when a tropical cyclone containing winds of 64 kt (74 mph) or higher poses a possible threat, generally within 36 hours. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.

The watch is issued for areas that border the Potomac River from Washington DC southward and for areas that border the Chesapeake Bay.

The watch does not mean that hurricane conditions will occur. It only means that these conditions are possible.

Hurricane Warning

A Hurricane Warning is issued when sustained winds of 64 kt (74 mph) or higher associated with a tropical cyclone are expected in 24 hours or less. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force.

The warning is issued for areas that border the Potomac River from Washington DC southward and for areas that border the Chesapeake Bay.

Wind Advisory

A Wind Advisory is issued when the following conditions are expected for 3 hours or longer.

1) sustained winds of 31 to 39 mph

AND/OR

2) wind gusts of 46 to 57 mph.

Hurricane Wind Watch

A Hurricane Wind Watch is issued for inland counties when there is a possibility that hurricane force winds (64 kt / 74 mph or higher) will move inland from the coast beyond areas that are covered by a Hurricane Watch. The watch does not mean that the hurricane force winds will occur. It just means that they are possible.

Hurricane Wind Warning

A Hurricane Wind Warning is issued when hurricane force winds (64 kt / 74 mph or higher) are expected to move inland from the coast beyond areas that are covered by a Hurricane Warning.

Small Craft Advisory

Small Craft Advisories are issued for the Tidal Potomac River and the Chesapeake Bay when one or both of the following conditions is expected to begin within 36 hours:

1) sustained winds of 18 knots to 33 knots, or frequent gusts between 18 knots and 33 knots.

OR

2) waves of 4 feet or higher

Gale Warning

Gale Warnings are issued for the Tidal Potomac River and the Chesapeake Bay when one or both of the following conditions is expected to begin within 36 hours:

1)  sustained winds of 34 knots to 47 knots

OR

2) frequent gusts between 34 knots and 47 knots.

Storm Warning

Storm Warnings are issued for the Tidal Potomac River and the Chesapeake Bay when one or both of the following conditions is expected to begin within 36 hours:

1)  sustained winds of 48 knots to 63 knots

OR

2) frequent gusts of 48 knots to 63 knots

Special Marine Warning

A warning of potentially hazardous weather conditions of short duration (up to 2 hours) affecting areas included in a CWF that are not adequately covered by existing marine warnings and producing one or more of the following:

• Sustained marine convective winds (showers/thunderstorms) or associated gusts of 34 knots or greater
• Hail three quarters of an inch or more in diameter
• Waterspouts

Severe Thunderstorm Watch

A Severe Thunderstorm Watch is issued when severe thunderstorms are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Severe thunderstorms are defined as follows:

Winds of 58 mph or higher

AND/OR

Hail 3/4 of an inch in diameter or larger.

Severe Thunderstorm Warning

A Severe Thunderstorm Warning is issued when severe thunderstorms are occurring or imminent in the warning area.

Severe thunderstorms are defined as follows:

Winds of 58 mph or higher

AND/OR

Hail 3/4 of an inch in diameter or larger.

Tornado Watch

A Tornado Watch is issued when severe thunderstorms and tornadoes are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Severe thunderstorms are defined as follows:

Winds of 58 mph or higher

AND/OR

Hail 3/4 of an inch in diameter or larger.

Tornado Warning

A Tornado Warning is issued when a tornado is imminent. When a tornado warning is issued, seek safe shelter immediately.

Tropical Storm Watch

A Tropical Storm Watch is issued when a tropical cyclone containing winds of 34 to 63 kt (39 to 73 mph) or higher poses a possible threat, generally within 36 hours. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.

The watch is issued for areas that border the Potomac River from Washington DC southward and for areas that border the Chesapeake Bay.

The watch does not mean that tropical storm conditions will occur. It only means that these conditions are possible.

Tropical Storm Warning

A Tropical Storm Warning is issued when sustained winds of 34 to 63 kt (39 to 73 mph) or higher associated with a tropical cyclone are expected in 24 hours or less. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.

The warning is issued for areas that border the Potomac River from Washington DC southward and for areas that border the Chesapeake Bay.

Tropical Storm Wind Watch

A Tropical Storm Wind Watch is issued for inland counties when there is a possibility that sustained winds of 34 to 63 kt (39 to 73 mph) may move inland from the coast beyond areas that are covered by a Tropical Storm Watch. The watch does not mean that the conditions will occur, just that they are possible.

Tropical Storm Wind Warning

A Tropical Storm Wind Warning is issued when sustained winds of 34 to 63 kt (39 to 73 mph) are expected to move inland from the coast beyond areas that are covered by a Tropical Storm Warning.

Coastal Flood Watch

Coastal Flood Watches are issued for areas along the Tidal Potomac River and areas along the Chesapeake Bay.

Coastal Flood Warning

A Coastal Flood Warning is issued when moderate to severe coastal flooding is occurring or imminent. This flooding will pose a serious risk to life and property.

Coastal Flood Warnings are issued for areas along the Tidal Potomac River and areas along the Chesapeake Bay.

Coastal Flood Advisory

A Coastal Flood Advisory is issued when minor or nuisance coastal flooding is occurring or imminent.

Coastal Flood Advisories are issued for areas along the Tidal Potomac River and areas along the Chesapeake Bay.

Flash Flood Watch

A Flash Flood Watch is issued when conditions are favorable for flash flooding. It does not mean that flash flooding will occur, but it is possible.

Flash Flood Warning

A Flash Flood Warning is issued when flash flooding is imminent or occurring.

Flood Watch

A Flood Watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible.

Flood Warning

A Flood Warning is issued when flooding is imminent or occurring.

River Flood Watch

A River Flood Watch is issued when river flooding is possible at one or more forecast points along a river.

River Flood Warning

A River Flood Warning is issued when river flooding is occurring or imminent at one or more forecast points along a river.

Excessive Heat Outlook

This is issued when the heat index value is expected to reach or exceed 110 degrees within the next 2 1/2 to 5 days.

Excessive Heat Watch

The Excessive Heat Watch shall be issued when the heat index value is expected to reach or exceed 110 degrees within the next 24 to 48 hours.

Excessive Heat Warning

The Excessive Heat Warning shall be issued when the heat index value is expected to reach or exceed 110 degrees within the next 12 to 24 hours.

Heat Advisory